Chapters 6(Final check at 9:00 AM 12/11/10) Microscopes
Magnification vs. resolving power
Magnification: ratio of object’s image size to its real size Resolving power: measure of clarity of image, the minimum distance 2 points can be separated and still be distinguished as 2 points
Electron microscopes
Disadvantages: can only view the surface, limited in magnification
Scanning electron microscopy
Detail of surface, electron beam scans sample, great depth (3-D)
Transmission electron microscopy Internal structure of cells, electron beam through section, pattern of transmitted electrons
Cell fractionation Whole cells broken up- smaller and smaller cell parts are isolated, isolate different organelles- study biochemical activities
Mitochondria= smallest organelles isolated
Cell structure
Bacteria and Archea consist of prokaryotic cells
Prokaryotic vs. eukaryotic cells: location of DNA Prokaryotic= DNA concentrated in nucleoid, no membrane separates from rest of cell Eukaryotic= nucleus in membranous nuclear envelope
Prokaryotic cell
Cell wall: rigid structure outside plasma membrane
Plasma membrane: encloses cytoplasm
Bacterial chromosome
Nucleoid: region of cell’s DNA
Cytoplasm
Flagella: locomotion organelles of some bacteria
Ribosomes: organelles that synthesize proteins
*Surface area to volume: higher surface to volume ratio= exchange of materials between cell and its environment= why cells are so small
Eukaryotic cell (genetic instructions based in nucleus and carried out by ribosomes)
Nuclear envelope= double membrane
Each bilayer with proteins
Chromatin= relaxed state
Chromosomes= condensed state
Nuclear lamina= lines nuclear side of envelope, protein filaments maintain shape of nucleus by supporting envelope
Nuclear matrix= fibers through nuclear interior
Chromosomes (found in nucleus, made of chromatin)
Chromatin= made of proteins and DNA
Cell prepares to divide4 chromatin becomes thick enough 4 chromosomes
Nucleoli are visible through electron microscopes as mass of granules/fibers
Ribosomal RNA are assembled
Ribosomes: carry out protein synthesis
Made of ribosomal RNA and protein
Type of Ribosome
Location
Product
Free ribosomes
Cytosol
Enzymes that catalyze first steps of sugar break down
Bound ribosomes
Outside of ER/nuclear envelope
Proteins- insertion in membranes/packaging lysosomes/export from cell
6.4: The Endomembrane system Structures: Endoplasmic reticulum (ER), Golgi apparatus, plasma membrane, lysosomes, vacuole Structure and Function of each structure: Endoplasmic reticulum: Structure: It is a network of tubes and chambers, called lumen. It has two regions, rough and smooth. The rough is studded with ribosomes, which help construct the proteins, and it is closer to the center of the cell. The smooth doesn’t have ribosomes and is more on outer regions. Transport vesicles are the little bubbles that surround the substances when they pinch off to go somewhere else, most likely the Golgi apparatus. Function: The rough synthesizes proteins, produces the membranes, and packages proteins to be secreted from the cell. The smooth makes phospholipids, lipids, and steroids; stores calcium ions (remember how this is where the calcium ions come from in muscle contraction); and breaks down harmful substances such as poisons. Remember that alcohol abuse leads to having more smooth ER, because the smooth is what detoxifies alcohol.
Golgi apparatus: Structure: It is a bunch of folded sacks. Cis and trans faces: these are the sides of the membrane that allow a vesicle to fuse with the plasma membrane of the cell for exocytosis. Function: This is the organelle that ships things where they need to go both within and outside the cell. The substance pinch off in little vesicles, which can fuse with the plasma membrane of other things to release the substance.
Lysosomes: This is a special vesicle that contains enzymes and it is used to break things down in the cell by fusing with their vesicles and breaking it down inside a contained vesicle. These are especially important in white blood cells because when the cell uses phagocytosis to take in something harmful, the lysosome will fuse with that vesicle to break down the harmful substance inside. Also, when something good inside the cell gets old and worn out such as an organelle, it will be enclosed in a vesicle so the lysosome can come and fuse to break it down.
Vacuoles: 3 types: Food vacuole (these are the pods that food comes into the cell in), contractile vacuole (fresh water single-celled organism use this to dump out excess water), and central vacuoles (holds the water in a plant cell to keep in turgid, also stores proteins and inorganic molecules).
6.5: Mitochondria and Chloroplasts and Peroxisomes Mitochondria: Structure: It has an outer membrane which surrounds the matrix, which is enclosed the inner membrane. The matrix has folds called cristae. There are ribosomes and mitochondria DNA in the mitochondria. The space between the outer and inner membrane is called the inner membrane space. Function: We have not fully covered it yet, but the mitochondria are responsible for cellular respiration which is making ATP by extracting energy.
Chloroplasts: Structure: It is surrounded by two membranes (the space between them is called the inner membrane space) and inside there are stacks, called granum, of little disks called thylakoids. In the space around them, called the stroma, there are ribosomes. Function: photosynthesis.
Peroxisomes: these organelles make peroxides which destroys things by taking electrons.
Be able to tell similarities and differences between mitochondria and chloroplasts (both have DNA and ribosomes and have double membranes; different functions)
6.6: The Cytoskeleton The cytoskeleton is all of the fibers that support, move, and regulate the cell. The fibers that make up the cytoskeleton are microtubules, microfilaments, and intermediate filaments. Microtubules: · They are made of hollow tubes made of tubulin (a protein) · Tubulin protein is a dimer made of two subunits. · Function of microtubules: maintenance, motility, organelle movements, chromosome movement in cell division · Each animal cell has a centrosome, which is made of two centrioles, which are made of microtubules. The structure of the centriole is supposed to be 9 sets of 3 microtubules. The two centrioles are perpendicular to each other. The function of the centrosome is believed to be the microtubule organizing center (MTOC). · Cilia and flagella are also made of microtubules and they are the motility of the cell. Cilia are smaller, there are a lot of them, and they move in a spinning pattern. The flagella are bigger and longer, there is only one or two of them and they undulate, or wave back and forth. The microtubules are arranged with 9 pairs of them around the side and one pair in the middle. The motor proteins called dyneins cause movement of cilia by using ATP to make the small dynein walk along the microtubules. · The basal body is what the cilia or flagella used to attatch to the cell and they are also made of microtubules. They are in the arrangement of 9 sets of 3 around the side and one in the middle. Microfilaments: · They are small and solid. · They are made from a double chain of actin. · Function: o Changes of cell shapes o Cytoplasm streaming o Muscle contraction: actin is the motor protein that slides the microfilaments to contract the muscle. o Cell division o Cell motility o Maintenance of cell shape Intermediate filaments: · Bigger than microfilaments but smaller than microtubules. · More permanently fixed in cells. · Made of keratin. · Functions: o Anchor some cell parts. o Support the nuclear lamina.
6.7: Extracellular Components Cell wall: · Functions: o Protect the plant cell o Maintain shape o Prevent the cell from filling up with too much water · Made of cellulose fibers and polysaccharides · Layers of the cell wall from the inside to the outside: o Plasma membrane o Secondary cell wall o Primary cell wall o Middle lamella (in between the cells; made of pectin) · Plant cells are connected by intercellular junctions called plasmodesmata. Large materials or small cell parts can pass through these connections.
Extracellular Matrix: Animals cells do not have a cell wall, but they do have an extracellular matrix. Along the bilayer phospholipid membrane, there are proteins called integrins, which are the things that the extracellular matrix on the outside and the microfilaments on the inside attach to. A little thing called the fibronectin attach the integrin to the large collagen fibers and the small proteoglycon complexes that make up the extracellular matrix. The proteoglycon complex is a polysaccharide molecule that looks like a branch with a protein core and carbohydrate fiber branches off of it.
Animal cells have three different types of intercellular junctions: tight junctions, desmosome anchoring, and gap junctions. · Tight junctions: This is layer of sealing of the cells that doesn’t let things through. · Desmosome anchoring: these are points of connection between the cells that hold them together. · Gap junction: these are tiny hole between the cells, kind of like the plasmodesmata, that allow materials to pass through.
Chapter 49
What are the essentials?
49. 6 Muscles move skeletal parts by contracting
1.Straited—Skeletal muscle is attached to bone and striated. It means the muscle is characterized by transverse stripes.
Look at Figure 49.28
A single muscle cell is also called a muscle fiber. Like a nested doll, each fiber contains the listed structure. Skeletal Muscle :responsible for the voluntary movement of the body
Myofibrils Important pictures: Figure 49.29, 49.30, 49.31
Sarcomere: The fundamental, repeating unit of striated muscle, delimited by the Z lines
Thick filaments: A filament composed of staggered arrays of myosin molecules; a component of myofibrils in muscle fibers.
Thin filaments: The smaller of the two myofilaments consisting of two strands of actin and two strands of regulatory protein coiled around one another.
3. The mechanism of muscle contraction is described by the sliding-filament model.
. Describe the myosin molecule:
Each myosin molecule consists of a long “tail” region and a globular “head” region extending to the side. The tail adheres to the tails of other myosin molecules that form the thick filament. The head is the center of bioenergetic reaction that power muscle contractions. It can bind ATP and hydrolyze it into ADP and inorganic Phosphate.
5. As you can see in Figure 40.30, musce contraction occurs when actin and myosin interact. Myosin heads bind to actin, forming cross-bridges. What molecule binds to myosin to provide the energy of contraction?
ATP!
6.In the relaxed muscle fiber, the myosin-binding sites are blocked by a regulatory proteins bound to the actin.
7. In a muscle fiber, the specialized endoplasmic reticulum is known as: sacroplasmic reticulum 8. What causes the release of Ca 2+ ? Nerve impulse 9. As you will learn in Chapter 48 on the nerve impulse transmission, an action potential will cause release of neurotransmitter at the stimulated neutron’s synaptic terminal. mportant picture: Figure 49.33
10.Steps of Muscle Contraction: 1. Nerve impulse arrives at the neuromuscular junction. 2. Acetylcholine is released from synaptic vesicles. 3. Acetylcholine binds to receptors on the muscle fibers. This allows Na + ions to rush, causing depolarization. 4. Depolarization continues across the sarcolemma and down the transverse tubule system. 5. Ca2+ is released from the cisterns of the SR (sacroplasmic reticulum) 6. Calcium ions bind to troponin molecules of thin filaments. 7. The troponin/tropomyosin complex is moved so the myosin-binding site of actin is exposed. 8. In the presence of Ca2+, myosin acts as an enzyme. It catalyses breakdown of ATP. Energy is transferred from ATP to the myosin head; myosin is activated. 9. Myosin head rotates bind the actin, and pull the actin fibers toward the center of the sarcomere.
11.What is meant by a motor unit?
A motor unit is a single motor neuron and all the muscle fibers it controls.
When a motor neutron produces an action potential, all the muscle fibers in its motor unit contracts as a group. The strength of the resulting contraction therefore depends on how many muscle fibers the motor neuron controls.
12. The three tyoes of muscles are skeletal, cardiac, and smooth.
a) cardiac muscle has intercalated disks
b) smooth muscle lacks striations.
c)skeletal muscle is striated and voluntary
d) skeletal muscle has both fast-twitch and slow-twitch fibers.
e) cardiac muscle is associated with the heart.
Chapter 49 – Sensory and Motor Mechanisms
Section 49.6 · Skeletal Muscles- bundles of multinucleated muscle cells, called fibers, that run the length of the muscle. o they are striated: they have strips of microfilaments that alternate light, dark, light, dark, etc. · Myofibrils- what make up the bundle of fibrils. They are composed of myofilaments. · Myofilaments o Thin filaments- two strands of actin coiled around one strand of regulatory protein. o Thick filaments- myosin molecules. · Sarcomere- the muscle unit. The repeating units of striated muscle. · Z Lines- border the Sarcomere. · A Band- thick filaments lying in the center of the muscle · H Zone- a place in the center where the thin filaments cannot reach · I Band- made of only thin filaments. When the muscle is at rest, the thick filaments cannot reach the I band.
Figure 49.28 · Tropomyosin- a regulatory protein that blocks the myosin-binding sites of the actin molecules when the muscle is at rest. · Troponin Complex- the set of regulatory proteins that controls the Tropomyosin. · Sarcoplasmic reticulum- where the calcium ions are transported. · T (transverse) tubules- infoldings of the muscle cell plasma membrane where the action potential is spread. · Motor Unit- a single motor neuron and all the muscle fibers it supplies with nerves. · Myoglobin- a pigment that subtracts oxygen from the blood and stores it.
Figures 49.30 and 49.31 DIFFERENT TYPES OF MUSCLE · Cardiac Muscle- muscle in the heart. Has intercalated discs where action potentials can spread to cells of the heart. · Smooth Muscle- non-striated muscle. It lacks T tubules, a troponin complex, and (a well developed) sarcoplasmic reticulum.
ord Roots! Myo- muscle Fibro- fiber
These steps are a mix of pg 197-198 in Cliffs book and Chapter 49 guided reading notes:
Neurons form specialized synapses with muscles called neuromuscular junctions. Muscle contraction is stimulated through the following steps:
1) Action Potential generates release of acetylcholine. When an action potential of a neuron (aka nerve impulse) reaches the neuromuscular junction, the neuron secretes the neurotransmitter acetylcholine, which diffuses across the synaptic cleft. 2) Action potential is generated on sarcolemma and throughout the T-tubules. Receptors on the sarcolemma initiate a depolarization event and action potential (the binding of acetylcholine on the receptors allows sodium ions to rush - > causing depolarization). The action potential travels along the sarcolemma throughout the transverse system of tubules. 3) Sarcoplasmic reticulum releases Ca2+. As a result of the action potential throughout the transverse system of tubules, the sarcoplasmic reticulum releases Ca2+. (Calcium ions releases from cisterns of the SR). 4) Myosin cross bridges form. The Ca2+ released by the sarcoplasmic reticulum binds to troponin molecules on the actin helix (thin filaments), prompting tropomyosin molecules to expose binding sites for myosin cross-bridge formation. If ATP is available, muscle contraction begins.
Sliding-filament Model
- Muscle contraction is described by the sliding-filament model:
1) ATP binds to a myosin head and forms ADP + Pi. When ATP binds to a myosin head, it is converted to ADP and Pi, which remain attached to the myosin head. 2) Ca2+ exposes the binding sites on the actin filaments. Ca2+ binds to the troponin molecule causing tropomyosin to expose positions on the actin filament for the attachment of myosin heads. 1) Cross bridges between myosin heads and actin filaments form. When attachment sites on the actin are exposed, the myosin heads bind to actin to form cross bridges. (In the presence of Ca++, myosin acts as an enzyme. It catalyzes breakdown of ATP. Energy is transferred from ATP to the myosin head; myosin is activated)
3) ADP and Pi are released and sliding motion of actin results. The attachment of cross bridges between myosin and actin causes the release of ADP and Pi. This, in turn, causes a change in shape of the myosin head, which generates a sliding movement of the actin toward the center of the sarcomere. This pulls the two Z-lines together, effectively contracting the muscle fiber. 4) ATP causes the cross bridges to unbind. When a new ATP molecule attaches to the myosin head, the cross bridge between the actin and myosin breaks, returning the myosin head to its unattached position.
Figure 49.33
Without the addition of a new ATP molecule, the cross bridges remain attached to the actin filaments. This is why corpses are stiff (new ATP molecules are unavailable).
Microscopes
Magnification vs. resolving power
Magnification: ratio of object’s image size to its real size
Resolving power: measure of clarity of image, the minimum distance 2 points can be separated and still be distinguished as 2 points
Electron microscopes
Disadvantages: can only view the surface, limited in magnification
Scanning electron microscopy
Detail of surface, electron beam scans sample, great depth (3-D)
Transmission electron microscopy
Internal structure of cells, electron beam through section, pattern of transmitted electrons
Cell fractionation
Whole cells broken up- smaller and smaller cell parts are isolated, isolate different organelles- study biochemical activities
Mitochondria= smallest organelles isolated
Cell structure
Bacteria and Archea consist of prokaryotic cells
Prokaryotic vs. eukaryotic cells: location of DNA
Prokaryotic= DNA concentrated in nucleoid, no membrane separates from rest of cell
Eukaryotic= nucleus in membranous nuclear envelope
Prokaryotic cell
Cell wall: rigid structure outside plasma membrane
Plasma membrane: encloses cytoplasm
Bacterial chromosome
Nucleoid: region of cell’s DNA
Cytoplasm
Flagella: locomotion organelles of some bacteria
Ribosomes: organelles that synthesize proteins
*Surface area to volume: higher surface to volume ratio= exchange of materials between cell and its environment= why cells are so small
Eukaryotic cell (genetic instructions based in nucleus and carried out by ribosomes)
Nuclear envelope= double membrane
Each bilayer with proteins
Chromatin= relaxed state
Chromosomes= condensed state
Nuclear lamina= lines nuclear side of envelope, protein filaments maintain shape of nucleus by supporting envelope
Nuclear matrix= fibers through nuclear interior
Chromosomes (found in nucleus, made of chromatin)
Chromatin= made of proteins and DNA
Cell prepares to divide4 chromatin becomes thick enough 4 chromosomes
Nucleoli are visible through electron microscopes as mass of granules/fibers
Ribosomal RNA are assembled
Ribosomes: carry out protein synthesis
Made of ribosomal RNA and protein
6.4: The Endomembrane system
Structures: Endoplasmic reticulum (ER), Golgi apparatus, plasma membrane, lysosomes, vacuole
Structure and Function of each structure:
Endoplasmic reticulum:
Structure: It is a network of tubes and chambers, called lumen. It has two regions, rough and smooth. The rough is studded with ribosomes, which help construct the proteins, and it is closer to the center of the cell. The smooth doesn’t have ribosomes and is more on outer regions. Transport vesicles are the little bubbles that surround the substances when they pinch off to go somewhere else, most likely the Golgi apparatus.
Function: The rough synthesizes proteins, produces the membranes, and packages proteins to be secreted from the cell. The smooth makes phospholipids, lipids, and steroids; stores calcium ions (remember how this is where the calcium ions come from in muscle contraction); and breaks down harmful substances such as poisons. Remember that alcohol abuse leads to having more smooth ER, because the smooth is what detoxifies alcohol.
Golgi apparatus:
Structure: It is a bunch of folded sacks. Cis and trans faces: these are the sides of the membrane that allow a vesicle to fuse with the plasma membrane of the cell for exocytosis.
Function: This is the organelle that ships things where they need to go both within and outside the cell. The substance pinch off in little vesicles, which can fuse with the plasma membrane of other things to release the substance.
Lysosomes: This is a special vesicle that contains enzymes and it is used to break things down in the cell by fusing with their vesicles and breaking it down inside a contained vesicle. These are especially important in white blood cells because when the cell uses phagocytosis to take in something harmful, the lysosome will fuse with that vesicle to break down the harmful substance inside. Also, when something good inside the cell gets old and worn out such as an organelle, it will be enclosed in a vesicle so the lysosome can come and fuse to break it down.
Vacuoles:
3 types: Food vacuole (these are the pods that food comes into the cell in), contractile vacuole (fresh water single-celled organism use this to dump out excess water), and central vacuoles (holds the water in a plant cell to keep in turgid, also stores proteins and inorganic molecules).
6.5: Mitochondria and Chloroplasts and Peroxisomes
Mitochondria:
Structure: It has an outer membrane which surrounds the matrix, which is enclosed the inner membrane. The matrix has folds called cristae. There are ribosomes and mitochondria DNA in the mitochondria. The space between the outer and inner membrane is called the inner membrane space.
Function: We have not fully covered it yet, but the mitochondria are responsible for cellular respiration which is making ATP by extracting energy.
Chloroplasts:
Structure: It is surrounded by two membranes (the space between them is called the inner membrane space) and inside there are stacks, called granum, of little disks called thylakoids. In the space around them, called the stroma, there are ribosomes.
Function: photosynthesis.
Peroxisomes: these organelles make peroxides which destroys things by taking electrons.
Be able to tell similarities and differences between mitochondria and chloroplasts (both have DNA and ribosomes and have double membranes; different functions)
6.6: The Cytoskeleton
The cytoskeleton is all of the fibers that support, move, and regulate the cell. The fibers that make up the cytoskeleton are microtubules, microfilaments, and intermediate filaments.
Microtubules:
· They are made of hollow tubes made of tubulin (a protein)
· Tubulin protein is a dimer made of two subunits.
· Function of microtubules: maintenance, motility, organelle movements, chromosome movement in cell division
· Each animal cell has a centrosome, which is made of two centrioles, which are made of microtubules. The structure of the centriole is supposed to be 9 sets of 3 microtubules. The two centrioles are perpendicular to each other. The function of the centrosome is believed to be the microtubule organizing center (MTOC).
· Cilia and flagella are also made of microtubules and they are the motility of the cell. Cilia are smaller, there are a lot of them, and they move in a spinning pattern. The flagella are bigger and longer, there is only one or two of them and they undulate, or wave back and forth. The microtubules are arranged with 9 pairs of them around the side and one pair in the middle. The motor proteins called dyneins cause movement of cilia by using ATP to make the small dynein walk along the microtubules.
· The basal body is what the cilia or flagella used to attatch to the cell and they are also made of microtubules. They are in the arrangement of 9 sets of 3 around the side and one in the middle.
Microfilaments:
· They are small and solid.
· They are made from a double chain of actin.
· Function:
o Changes of cell shapes
o Cytoplasm streaming
o Muscle contraction: actin is the motor protein that slides the microfilaments to contract the muscle.
o Cell division
o Cell motility
o Maintenance of cell shape
Intermediate filaments:
· Bigger than microfilaments but smaller than microtubules.
· More permanently fixed in cells.
· Made of keratin.
· Functions:
o Anchor some cell parts.
o Support the nuclear lamina.
6.7: Extracellular Components
Cell wall:
· Functions:
o Protect the plant cell
o Maintain shape
o Prevent the cell from filling up with too much water
· Made of cellulose fibers and polysaccharides
· Layers of the cell wall from the inside to the outside:
o Plasma membrane
o Secondary cell wall
o Primary cell wall
o Middle lamella (in between the cells; made of pectin)
· Plant cells are connected by intercellular junctions called plasmodesmata. Large materials or small cell parts can pass through these connections.
Extracellular Matrix:
Animals cells do not have a cell wall, but they do have an extracellular matrix. Along the bilayer phospholipid membrane, there are proteins called integrins, which are the things that the extracellular matrix on the outside and the microfilaments on the inside attach to. A little thing called the fibronectin attach the integrin to the large collagen fibers and the small proteoglycon complexes that make up the extracellular matrix. The proteoglycon complex is a polysaccharide molecule that looks like a branch with a protein core and carbohydrate fiber branches off of it.
Animal cells have three different types of intercellular junctions: tight junctions, desmosome anchoring, and gap junctions.
· Tight junctions: This is layer of sealing of the cells that doesn’t let things through.
· Desmosome anchoring: these are points of connection between the cells that hold them together.
· Gap junction: these are tiny hole between the cells, kind of like the plasmodesmata, that allow materials to pass through.
Chapter 49
What are the essentials?49. 6 Muscles move skeletal parts by contracting
1.Straited—Skeletal muscle is attached to bone and striated. It means the muscle is characterized by transverse stripes.
Look at Figure 49.28
A single muscle cell is also called a muscle fiber. Like a nested doll, each fiber contains the listed structure.
Skeletal Muscle :responsible for the voluntary movement of the body
Myofibrils
Important pictures:
Figure 49.29, 49.30, 49.31
Sarcomere: The fundamental, repeating unit of striated muscle, delimited by the Z lines
Thick filaments: A filament composed of staggered arrays of myosin molecules; a component of myofibrils in muscle fibers.
Thin filaments: The smaller of the two myofilaments consisting of two strands of actin and two strands of regulatory protein coiled around one another.
3. The mechanism of muscle contraction is described by the sliding-filament model.
. Describe the myosin molecule:
Each myosin molecule consists of a long “tail” region and a globular “head” region extending to the side. The tail adheres to the tails of other myosin molecules that form the thick filament. The head is the center of bioenergetic reaction that power muscle contractions. It can bind ATP and hydrolyze it into ADP and inorganic Phosphate.
5. As you can see in Figure 40.30, musce contraction occurs when actin and myosin interact. Myosin heads bind to actin, forming cross-bridges. What molecule binds to myosin to provide the energy of contraction?
ATP!
6.In the relaxed muscle fiber, the myosin-binding sites are blocked by a regulatory proteins bound to the actin.
7. In a muscle fiber, the specialized endoplasmic reticulum is known as: sacroplasmic reticulum
8. What causes the release of Ca 2+ ? Nerve impulse
9. As you will learn in Chapter 48 on the nerve impulse transmission, an action potential will cause release of neurotransmitter at the stimulated neutron’s synaptic terminal.
mportant picture: Figure 49.33
10.Steps of Muscle Contraction:
1. Nerve impulse arrives at the neuromuscular junction.
2. Acetylcholine is released from synaptic vesicles.
3. Acetylcholine binds to receptors on the muscle fibers. This allows Na + ions to rush, causing depolarization.
4. Depolarization continues across the sarcolemma and down the transverse tubule system.
5. Ca2+ is released from the cisterns of the SR (sacroplasmic reticulum)
6. Calcium ions bind to troponin molecules of thin filaments.
7. The troponin/tropomyosin complex is moved so the myosin-binding site of actin is exposed.
8. In the presence of Ca2+, myosin acts as an enzyme. It catalyses breakdown of ATP. Energy is transferred from ATP to the myosin head; myosin is activated.
9. Myosin head rotates bind the actin, and pull the actin fibers toward the center of the sarcomere.
11.What is meant by a motor unit?
A motor unit is a single motor neuron and all the muscle fibers it controls.
When a motor neutron produces an action potential, all the muscle fibers in its motor unit contracts as a group. The strength of the resulting contraction therefore depends on how many muscle fibers the motor neuron controls.
12. The three tyoes of muscles are skeletal, cardiac, and smooth.
a) cardiac muscle has intercalated disks
b) smooth muscle lacks striations.
c)skeletal muscle is striated and voluntary
d) skeletal muscle has both fast-twitch and slow-twitch fibers.
e) cardiac muscle is associated with the heart.
Chapter 49 – Sensory and Motor Mechanisms
Section 49.6
· Skeletal Muscles- bundles of multinucleated muscle cells, called fibers, that run the length of the muscle.
o they are striated: they have strips of microfilaments that alternate light, dark, light, dark, etc.
· Myofibrils- what make up the bundle of fibrils. They are composed of myofilaments.
· Myofilaments
o Thin filaments- two strands of actin coiled around one strand of regulatory protein.
o Thick filaments- myosin molecules.
· Sarcomere- the muscle unit. The repeating units of striated muscle.
· Z Lines- border the Sarcomere.
· A Band- thick filaments lying in the center of the muscle
· H Zone- a place in the center where the thin filaments cannot reach
· I Band- made of only thin filaments. When the muscle is at rest, the thick filaments cannot reach the I band.
Figure 49.28
· Tropomyosin- a regulatory protein that blocks the myosin-binding sites of the actin molecules when the muscle is at rest.
· Troponin Complex- the set of regulatory proteins that controls the Tropomyosin.
· Sarcoplasmic reticulum- where the calcium ions are transported.
· T (transverse) tubules- infoldings of the muscle cell plasma membrane where the action potential is spread.
· Motor Unit- a single motor neuron and all the muscle fibers it supplies with nerves.
· Myoglobin- a pigment that subtracts oxygen from the blood and stores it.
Figures 49.30 and 49.31
DIFFERENT TYPES OF MUSCLE
· Cardiac Muscle- muscle in the heart. Has intercalated discs where action potentials can spread to cells of the heart.
· Smooth Muscle- non-striated muscle. It lacks T tubules, a troponin complex, and (a well developed) sarcoplasmic reticulum.
ord Roots!
Myo- muscle
Fibro- fiber
These steps are a mix of pg 197-198 in Cliffs book and Chapter 49 guided reading notes:
Neurons form specialized synapses with muscles called neuromuscular junctions. Muscle contraction is stimulated through the following steps:
1) Action Potential generates release of acetylcholine. When an action potential of a neuron (aka nerve impulse) reaches the neuromuscular junction, the neuron secretes the neurotransmitter acetylcholine, which diffuses across the synaptic cleft.
2) Action potential is generated on sarcolemma and throughout the T-tubules. Receptors on the sarcolemma initiate a depolarization event and action potential (the binding of acetylcholine on the receptors allows sodium ions to rush - > causing depolarization). The action potential travels along the sarcolemma throughout the transverse system of tubules.
3) Sarcoplasmic reticulum releases Ca2+. As a result of the action potential throughout the transverse system of tubules, the sarcoplasmic reticulum releases Ca2+. (Calcium ions releases from cisterns of the SR).
4) Myosin cross bridges form. The Ca2+ released by the sarcoplasmic reticulum binds to troponin molecules on the actin helix (thin filaments), prompting tropomyosin molecules to expose binding sites for myosin cross-bridge formation. If ATP is available, muscle contraction begins.
Sliding-filament Model
- Muscle contraction is described by the sliding-filament model:
1) ATP binds to a myosin head and forms ADP + Pi. When ATP binds to a myosin head, it is converted to ADP and Pi, which remain attached to the myosin head.
2) Ca2+ exposes the binding sites on the actin filaments. Ca2+ binds to the troponin molecule causing tropomyosin to expose positions on the actin filament for the attachment of myosin heads.
1) Cross bridges between myosin heads and actin filaments form. When attachment sites on the actin are exposed, the myosin heads bind to actin to form cross bridges. (In the presence of Ca++, myosin acts as an enzyme. It catalyzes breakdown of ATP. Energy is transferred from ATP to the myosin head; myosin is activated)
3) ADP and Pi are released and sliding motion of actin results. The attachment of cross bridges between myosin and actin causes the release of ADP and Pi. This, in turn, causes a change in shape of the myosin head, which generates a sliding movement of the actin toward the center of the sarcomere. This pulls the two Z-lines together, effectively contracting the muscle fiber.
4) ATP causes the cross bridges to unbind. When a new ATP molecule attaches to the myosin head, the cross bridge between the actin and myosin breaks, returning the myosin head to its unattached position.
Figure 49.33
Without the addition of a new ATP molecule, the cross bridges remain attached to the actin filaments. This is why corpses are stiff (new ATP molecules are unavailable).